This invention relates to fences assembled from so-called self-adjusting or self-raking panels, each comprising a plurality of pales supported by two or more rails.
Self-raking fence panels are arranged to permit the pales to be pivotably adjusted through a limited angular range with respect to the rails, so that the rails can be fixed between adjacent vertical posts and adjusted or “raked” to follow the slope of the ground. Once installed, it is important that the fence is as difficult as possible for unauthorised persons to dismantle, so that it can resist vandalism and, where required, provide a secure barrier. Preferably, the number and complexity of the component parts should be minimised, so as to reduce the cost of manufacture and assembly.
Since each pale is pivotably connected to the rails, a self-raking panel is inherently less rigid than a panel with welded joints. It is therefore particularly important to ensure that the panels do not sag under their own weight and that the pales do not rattle in the rails, since this can make the fence appear weak and untidy. For this reason an anti-sag support is often installed in the ground in the middle of each panel.
It is known to assemble self-raking panels by riveting each pale to a rail formed from an angled bar, so that the rivets form pivots about which each pale can move. However, the rivets must be inserted and closed one by one, which is slow and expensive, and are found to be vulnerable to removal by a cold chisel or by levering with a scaffold pole inserted between the pales after the fence is erected.
Moreover, such panels must be assembled in a factory and then transported to the site on which the fence is to be erected. Each panel may be, for example, 2.5 m or more in length and 50 kg or more in weight, and occupies considerably more volume during transportation than the sum of its individual components. Depending on the distance from the factory to the site, the cost of transportation may considerably increase the cost of the finished fence.
Once on site, the site must be carefully measured and the posts erected so that the correct spacing is maintained between each pair of adjacent posts to receive the pre-assembled panels. Moreover, the weight of each panel may cause serious injury to fingers trapped between the rails and the pales, particularly in the aperture through which each pale passes, as the panel is raked. It is therefore desirable to install pre-assembled panels using specially trained workers, which further increases cost, especially where the fence is to be installed at a significant distance from the factory.
GB 2 435 055 (published after the priority date of the present application) discloses a self-raking fence panel comprising a plurality of fence members (pales) which are received in tubular rails of hollow box section. A deformable support member, comprising a length of resilient channel section with converging side walls, is inserted into the rail prior to assembly of the pales, and engages a dowel inserted into each pale to retain the pale in the rail. After installation, the pale is free to move longitudinally in the rail.
In alternative embodiments GB '055 proposes that a support member may be integrally formed with a rail, and the rail itself may comprise a channel section with a portion of one or both side walls that either converge or diverge, which side walls are resiliently urged apart.
U.S. Pat. No. 2,218,954 discloses a fence panel in which the rail itself is formed as a flexible channel section in which the lower portions are inturned to resiliently engage the pickets (pales). The rails are first installed in position, and then the pickets are inserted one by one through apertures in the rails so that the side walls are resiliently urged apart so as to engage in slots in the pales.
The posts, rails and pales can thus be transported in bundles to the site, where the posts and rails are erected before inserting the pales into the rails. However, once the fence is assembled there is little to prevent it from being dismantled by reversing the procedure. Moreover, the use of inherently flexible, deformable rails can be expected to reduce the rigidity of the finished panel.
A more rigid and secure self-raking panel having pales with fixed, transverse pins is available under the trade name “Atlas” (™) from Heras Nederland BV (www.heras.nl). Each rail is a hollow box section having aligned apertures spaced along its upper and lower walls. Each pair of apertures is provided with a tubular plastics sleeve which extends between the upper and lower walls of the rail to receive one of the pales. Each of the side walls of the sleeve is spaced apart from the adjacent outer side wall of the rail and is slotted to define a pair of resiliently deformable flaps and a hole for receiving one end of the transverse pin. Each pale is inserted through the corresponding sleeves in the upper and lower rails and then rotated so that the projecting ends of each fixed, transverse pin urge the flaps outwardly to accommodate the pin as it enters the holes.
Once in place, the pin is concealed within the rail and the pale is difficult to remove. However, the plastics inserts increase the component count and cost of the panel, and may be damaged by heat.
WO 02/072982 discloses a self-raking panel with rigid, invert, U-shaped rails, each defining a downwardly open channel in which the side walls are integral with inner, return walls which extend upwardly between the side walls. Pairs of recesses are formed in the upper edges of the inner return walls and aligned in the transverse direction of the rail. Each pale has at least one fixed transverse pin, and is inserted through an aperture in the top wall of each rail and then rotated so that the projecting ends of each pin enter the recesses. An angled locking bar is then inserted between an adjacent return wall and sidewall of the rail so that its upper leg occupies a gap between the upper edge of the return wall and the top wall of the rail, trapping the pins in the recesses.
The panel may be assembled on site by arranging the rails and pales on the ground and then inserting the locking bar from one end of each rail. In practice, the angled bar is found to be difficult to insert due to its length and the frictional resistance of the rail, so that factory assembly is preferred.
EP 1 016 768 B1 discloses a self-raking panel in which each of the tubular metal pales is fitted with a resilient clip whose ends extend through opposed openings in the pale wall to provide a pivot. The rail comprises a rigid, invert U-shaped channel having a horizontal top wall and inner return walls between the outer side walls. The pales are inserted through apertures in the top wall so that the openings in the pale wall are aligned with corresponding recesses in the return walls, which receive the ends of the clip. In practice it is found to be difficult to compress the clips by rotating the pale in the rails, so panels of this type are in practice assembled at the factory using a jig which aligns the pales with the rails before a specialist tool is used to insert the clips into the ends of the pales.